The present invention generally relates to diverters and in particular to a diverter flowline seal used in subsea drilling.
Installing large diameter elastomeric diverter flowline seals can often be difficult since compressing a substantial amount of rubber into sealing position can require substantial force that is not always available. Also, stabbing an external piston type seal into a bore without damaging the seal or surrounding hardware is difficult when the diameters of the seal and surrounding hardware are equal to or greater than the receiving bore diameter. Unidirectional elastomeric seals such as a lip seal can be used to alleviate stabbing problems since they do not require cross-sectional compression of the elastomeric material by utilizing a lip that can easily be bent inward. However, many seal applications require bidirectional sealing and using two lip seals is not desirable since one lip seal must be stabbed in a direction that could snag the lip.
A diverter flowline seal used in subsea drilling that must be stabbed into a mating bore, is an example of a large diameter seal that is difficult to install. A common practice is to use an inflatable seal that, in its preinstalled state, has significant clearance with the mating bore, and when inflated with auxiliary fluid pressure, expands to firmly engage and seal against the bore. This type of seal is easy to install and once inflated provides bidirectional sealing.
Conventional diverter flowline seal designs rely on rigid metal end rings partitioned by a bonded elastomeric sealing element which can be slipped onto and retained on a stabbing mandrel. Elastomeric seals such as o-rings form a seal between the inner diameter of the metal rings and the exterior of the stabbing mandrel. A channel within the stabbing mandrel transmits auxiliary fluid pressure between the two end ring seals and inflates the bonded elastomeric section of the flowline seal assembly after the mandrel is stabbed into position. The inflated bonded elastomeric section expands to contact the receiving bore and a bidirectional seal is created between the diverter flowline seal and the receiving bore. An inherent weakness in this design, however, is located at the bonded boundary between the rigid metal end rings and the inflatable elastomeric section. Fatigue at this highly stressed boundary causes bond separation or tearing of the elastomeric sealing element and initiates a leak.
Another conventional diverter flowline seal design is shown in U.S. Pat. Nos. 5,890,535 and 6,290,231. The diverter flowline seal design shown in these patents eliminates the potential leakage across the bonded area between the rigid metal end rings and the inflatable elastomeric section by moving the sealing bead of the internal seals that seal off against the stabbing mandrel from the inner diameters of the metal rings to lip seals that are formed within the bonded elastomeric section. Shoulders extending from the rigid metal end rings extend over the internal lip seals and restrict expansion of the lip diameters during inflation. The contrasting material modulus at the boundaries of the rigid metal end rings and the inflatable elastomeric section, however, still creates high stress concentrations with the elastomeric section and can initiate tearing at this boundary.